Railroad locomotives, as well as other vehicles, commonly employ engine systems that may include an exhaust gas recirculation (EGR) system associated therewith. The EGR system is configured to reduce emissions and increase efficiency of the engine system by recirculating a part of the exhaust gases to an air intake system of the engine. The engine is typically a turbocharged internal combustion engine, which generates considerable heat when operating. If not properly dissipated, this heat reduces the operating efficiency of the engine and can ultimately result in damage to the engine. It is known to provide engine cooling systems having a first cooling circuit, sometimes called a jacket water cooling circuit, which flows a coolant through channels in the engine block to cool the engine. The coolant captures heat from the engine and releases the heat via a radiator through which the coolant eventually passes. The coolant may be pumped through various engine components, including the engine oil cooler, to capture heat from each of the components.
It is also known to provide a second cooling circuit in an engine cooling system that flows coolant through intercoolers and aftercoolers associated with the engine turbochargers. Specifically, the use one or more turbochargers for compressing air to be supplied to one or more combustion chambers within the engine cylinders is common. The turbocharger supplies combustion air or charge air at a higher pressure and higher density than existing atmospheric pressure and ambient density. Compression of air by the turbocharger also significantly increases its temperature. To overcome the detrimental effects of the increase in temperature, intercoolers have been provided in the charge air flow path between compressors of the turbocharger system. Similarly, aftercoolers have been used further downstream in turbocharger systems having both single stage and multi-stage compressors. The aftercooler cools the compressed air being supplied to the intake manifold of the engine to better support combustion in the cylinders and to decrease engine operating temperatures. This second cooling circuit, sometimes called a charge air cooling circuit, circulates coolant through the intercooler/aftercooler components, providing a heat exchange medium for the compressed air also flowing through these components. Heat from the compressed air captured by this coolant may also be released via a radiator.
Locomotives and other machines operate in a variety of environments, including in cold weather where ambient temperatures may fall to below the freezing point of water. When not operating, the heat of the engine system, especially in a cold ambient environment, will dissipate rapidly. Also, in cases where the engine is operating at an ambient temperature below freezing, the coolant itself may approach a freezing temperature. In such conditions, the coolant, typically water, may freeze within the cooling system causing damage to the components of the engine system. Because of this potential problem, it is known to equip engine cooling systems with a drain line having a valve thereon. For example, either or both of the above-described first and second cooling circuits may be provided with individual drain lines. The drain lines may intersect or merge downstream proximate a drain valve disposed on a common drain line. The drain valve may be a temperature responsive valve that opens to drain coolant when a certain low temperature threshold is met. For example, should the coolant temperature drop to below around 35-40° F., the drain valve may open to allow drainage of coolant from the system. Drain valves are typically located at a low gravitational point relative to the cooling circuits such that all of the coolant can drain out of the coolant systems when such valves are opened.
This method of draining coolant from the two cooling circuits functions adequately for avoiding freeze-ups of coolant in the engine system; however, there remains room for improvement. While water is typically used as the coolant in both the first and second cooling circuits described above, for maximized efficiency, the water for each circuit is preferably maintained at significantly different temperatures. For example, depending on the ambient temperature, the jacket water coolant should be maintained at a temperature above 180° F., while the charge air coolant should be maintained at a temperature above the ambient temperature but much lower than the jacket water coolant temperature. For this reason, it is preferable that the coolants of the two different circuits are not allowed to mix.
However, in locomotive applications, the mixing of the two water coolants has been common, decreasing the efficiency of the engine system. Specifically, when the engine is operating normally and the drain valve is closed, the coolants of the two different circuits are allowed to mix together in the common drain line. While only a small percentage of the two coolants mix in this drain line, this drain line is in fluid communication with the entirety of the two cooling circuits. As such, any change in the coolants due to the mixing may be transferred to the entirety of the circuits. Mixing of jacket water coolant with charge air coolant results in a decrease in the jacket water coolant temperature and an increase in the charge air coolant temperature. For instance, it has been observed that the mixing of only five percent of the two coolants can cause the coolant in both circuits to approach the same temperature within a few minutes. This mixing of the two coolants may not only defeat the purpose of maintaining two independent circuits, it may cause a loss in the efficiency of both cooling circuits. However, circumstances may arise where intermittent mixing of coolants, and therefore, increasing the temperature of the charge air coolant may be advantageous.
For example, the mixing of the two coolants may be preferred during sub-freezing operations where the engine is only idling. In this case, there is no real heat addition to the charge air cooling system as there is no heat being generated by the compressor. This may lead to freezing of the coolant in the charge air cooling circuit as locomotives are oftentimes kept idling for days in cold environments in order to keep the water in the jacket water circuit above freezing. During such operations, it is preferable that the coolants of both cooling systems be allowed to mix in order to keep the coolant of the charge air cooling system above its freezing point. Accordingly, there remains a need in the industry for a system capable of providing both mixing of the coolants and/or draining of the coolants as needed, based upon the relevant temperatures.
The presently disclosed engine cooling systems and methods address one or more of the above-described problems and/or other problems in the art.